Monodirectional impeller with flexible vanes

ABSTRACT

A monodirectional impeller for centrifugal electric pumps having a permanent-magnet synchronous motor, having vanes which are deformable at least along part of their extension so as to change their curvature, when loaded, in one direction of rotation, so that the power required for rotation in that direction is greater than the maximum power that can be delivered by the motor.

BACKGROUND OF THE INVENTION

The present invention relates to a monodirectional impeller forcentrifugal electric pumps having a permanent-magnet synchronous motor.

It is known that permanent-magnet synchronous electric motors have ageneral structure which comprises a stator, provided with anelectromagnet constituted by a lamination pack and by correspondingwindings, and a rotor, which is arranged between two pole shoes formedby the stator and is crossed axially by a shaft which is rotatablyconnected to a supporting structure.

These motors are bidirectional, i.e., at startup the rotor can beinduced equally to turn clockwise or counterclockwise.

This characteristic depends on a plurality of factors, including thearrangement of the polarities of the rotor with respect to the magneticfield generated between the pole shoes of the stator pack when theinduction windings are supplied with AC current.

For this reason, permanent-magnet synchronous motors are currentlywidely used where the direction of rotation is not important;accordingly, for example they are coupled, in centrifugal pumps, toradial-vane impellers which ensure the same performance in bothdirections of rotation.

In order to increase the efficiency of synchronous-motor electric pumpswithout resorting to the use of particular electronic starting devices,it is convenient to use vanes which are orientated with a certaincurvature profile, which clearly presumes a single direction of rotationof the motor.

Accordingly, electronic starter devices have been devised which guidethe motor so that it starts in a single direction of rotation; as analternative thereto, mechanical devices have been devised which blockthe rotor when it tends to start in the wrong direction of rotation(reference should be made for example to patent application PD98A000003of Jan. 8, 1998 in the name of this same Applicant).

In this manner, monodirectional behavior is ensured in any operatingcondition assumed by the electric pump.

However, the system may generate noise during starting and is alimitation as regards reliability (for high-power pumps), since there isa mechanical device which is subjected to repeated stresses, especiallyduring starting.

A particularly important alternative for a monodirectional synchronouselectric pump without mechanical devices for stopping the rotor andwithout electronic devices (which are reliable but expensive) isconstituted by what is disclosed in patent application PD98A000058 ofMar. 19, 1998 in the name of this same Applicant.

This patent application discloses a device which is able to start, withlimited power levels, loads which have high moments of inertia, such asimpellers with orientated vanes of a centrifugal pump.

In particular, this is a driving device with a larger angle of freerotation between the rotor and the impeller, so as to obtain, withrespect to conventional mechanical couplings, several advantages:

reduction of the starting torque for starting the motor;

a consequent reduction of the level of vibrations generated duringsynchronous operation;

the motor is rendered monodirectional by means of the correct design ofthe vanes of the impeller, so that the power absorbed by the load in onedirection of rotation is greater than the available power of the motorand is smaller in the opposite direction of rotation.

Therefore, by designing the motor and the vanes of the impeller so thatthe power absorbed by the load in one direction of rotation is greaterthan the available power of the motor and smaller in the oppositedirection of rotation, in the first case the impeller goes out of stepwith respect to the motor, is halted and automatically reverses itsmotion, whereas in the second case it is driven normally.

It is thus possible to render the pump monodirectional by utilizing thedifference in power between what the motor is able to deliver and thepower absorbed by the load in the two directions of rotation (the rotorstops because the power required by the impeller in the wrong directionof rotation is greater than the power that the motor can deliver).

Although this system provides a fundamental advantage with respect tothe prior art, it still has limitations, because monodirectionality isensured only within a flow-rate/head range; accordingly, it is used inapplications where the hydraulic working point does not vary beyondcertain limits or, in other words, where the characteristic curve of theduct does not undergo significant variations (this is the case, forexample, of washing pumps for dishwashers).

In the accompanying drawings FIG. 1 plots, for both directions ofrotation of the motor, the power absorbed by the motor as a function ofthe required flow-rate.

The line A plots the correct direction of rotation, the line B plots thewrong direction of rotation, and the straight line C represents themaximum power that can be delivered by the motor.

The chart shows three flow-rates Q1, Q2 and Q3, which correspond tothree working points, and it is clear that only Q1 and Q2 are theflow-rates for which a single direction of rotation is ensured, sincethe maximum power that the motor is able to deliver (straight line C) isgreater than the power required by the impeller when it turns in thecorrect direction of rotation (line A) and is smaller than the powerrequired by the impeller when it turns in the opposite direction (lineB).

For the flow-rate Q3, instead, there is a condition in which both powerlevels, in both directions of rotation, are lower than the maximumdeliverable power and therefore monodirectional behavior is notpossible.

SUMMARY OF THE INVENTION

The aim of the present invention is therefore to eliminate theabove-noted drawbacks of the above-cited device related to patentapplication

Within this aim, a consequent primary object is to provide a pump whichis monodirectional over the entire available flow-rate range.

Another object is to provide all of the above in a constructively simplemanner.

Another object is to have no effect on noise levels.

Another object is to provide an impeller, if necessary, with deformablevanes enclosed between a double fluid conveyance wall (closed impeller).

This aim and these and other objects which will become better apparenthereinafter are achieved by an impeller for centrifugal electric pumpshaving a permanent-magnet synchronous motor, characterized in that itsvanes are deformable at least along part of their extension and canchange their curvature, when loaded, in one direction of rotation, sothat the power required for rotation in that direction is greater thanthe maximum power that can be delivered by the motor.

Conveniently, in one embodiment, this aim and these objects are achievedby an impeller for centrifugal electric pumps having a permanent-magnetsynchronous motor, characterized in that it comprises:

a first disk-like element provided with curved nondeformable vanes whichare monolithic therewith,

an annular element, whose dimensions are contained within the inletdimensions of said nondeformable vanes and which is provided with meansfor coupling to said first disk-like element, said annular element beingprovided with flexibly deformable vanes which cantilever outward, areinterposed between the nondeformable ones, and are adapted to modify,when loaded, their curvature in one of the directions of rotation sothat the power required for rotation in that direction is greater thanthe maximum power that can be delivered by the motor,

a second disk-like element, which encloses, together with said firstdisk-like element, the set of vanes and is rigidly coupled to saidnondeformable vanes, leaving the deformable ones free.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will becomebetter apparent from the detailed description of embodiments thereof,illustrated only by way of non-limitative example in the accompanyingdrawings, wherein:

FIG. 1 is a chart which plots, for conventional centrifugal pumps, theflow-rate as a function of the power required in the two directions ofrotation;

FIG. 2 is a sectional view of an impeller according to the invention ina first embodiment, arranged inside a volute of a centrifugal pump;

FIG. 3 is an exploded view of the components of FIG. 2;

FIG. 4 is a plan view of an impeller according to the invention in asecond embodiment;

FIG. 5 is a side view of the impeller of FIG. 4;

FIG. 6 is a sectional view of an impeller according to the invention ina third embodiment, arranged inside a volute of a centrifugal pump;

FIG. 7 is a chart which plots, for centrifugal pumps with impellersaccording to the invention, the flow-rate as a function of the powerrequired in the two directions of rotation;

FIG. 8 is a side view of another impeller according to the invention;

FIG. 9 is a front view of the impeller of FIG. 8;

FIG. 10 is an exploded perspective view of the impeller of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 2 and 3, in a first embodiment the impelleraccording to the invention comprises a disk 10 with a central hollowcup-shaped body 11 which is a component of a driving device 12 describedin greater detail hereinafter.

A plurality of vanes 13 protrudes from a ring 16 which is located on theoutside of the cup-shaped body 11 in a corresponding seat 10 a of thedisk 10.

The vanes 13 are monolithic with respect to the ring 16, which affectsonly their part that lies closest to the center.

The peripheral part can therefore perform flexing movements arising fromthe elastic characteristics of the material of which they are made.

The vanes 13 can also be rigidly coupled to the ring 16 (axial andtorsional retention) in various manners: by interlocking and/orinterference, ultrasonic welding, adhesive bonding.

The peripheral regions 14 of the vanes 13 are therefore flexiblydeformable, as mentioned, and said deformation is greater for the wrongdirection of rotation and is optionally limited by the stroke limitingteeth 15 which protrude from the disk 10 alternately with the vanes 13.

In order to center the vanes 13 with respect to the teeth 15, the ring16 has axial teeth 17 to be inserted in appropriately provided holes 18of the disk 10.

As regards the driving device 12, it comprises said hollow body 11 and acover 19 which can also be rigidly coupled to the ring 16 with the vanes13.

The hollow body 11 is provided with an axial hole 20 for the shaft 21 ofthe rotor, not shown in the figures, of the motor.

An O-ring gasket 23 acts on the shaft 21 and is accommodated in acorresponding seat of the hollow body 11.

The hermetic seal of the device 12 is ensured not only by the gasket 23but also by the closure of the lid 19, which is provided by ultrasonicwelding, adhesive bonding or other known methods on the hollow body 11.

It is possible to provide alternative embodiments which are not hermeticor in which the lid 19 is monolithic with the ring 16.

In said ring, a tooth 24 protrudes from the inner wall and is thereforerigidly coupled to the impeller assembly; said tooth 24 interacts with atooth 25 which protrudes from a ring 26 which can rotate about a shank27 which is mounted with interference on the shaft 21 and is rigidlycoupled thereto.

A tooth 28 protrudes radially from the shank 27 and interacts, in itsrotation, with the tooth 25 of the ring 26, whose axial extension issuch as to affect the path of the rotation of both teeth 24 and 25.

Said teeth are arranged axially so that they do not interfere with eachother.

Accordingly, the rotation of the shaft 21 starts the rotation of thetooth 28, makes said tooth interact with the tooth 25, turning it untilit interferes with the tooth 24, and finally makes the rotor turn theimpeller.

Grease, with a shock-absorbing function, can be conveniently placedinside the hollow body 11.

FIGS. 2 and 3 also illustrate the volute 29 in which the impeller isarranged.

With reference now to FIGS. 4 and 5, an impeller according to theinvention, in a second embodiment which is simplified with respect tothe preceding one, comprises a disk 110, from which a coaxial shank 111with a hole 112 for the shaft of the rotor (not shown for the sake ofsimplicity) protrudes centrally on one side, and from which a pluralityof vanes 113 with a curved profile protrudes on the other side.

The impeller as a whole is formed monolithically.

According to the invention, the vanes 113 are flexibly deformable alongat least part of their extension, so as to modify their curvature, whenloaded, in one of the two directions of rotation so that the powerrequired for rotation in that direction is greater than the maximumpower that can be delivered by the motor.

The deformability of the vanes arises from the flexibility of theirperipheral regions 114, which are provided separately from the disk 110by the molding step by way of an appropriate shaping of the mold.

By providing the impeller as a single part made of plastics, with theperipheral regions 114 divided from the rest, said regions flex, whenloaded, in the wrong direction of rotation and modify their curvature sothat in practice they block the rotation.

Conveniently, teeth 115 protrude from the disk 110 in the peripheralregion, are alternated with the vanes 113, and advantageously act asstop elements which avoid excessive curvatures of said vanes 113 in thewrong direction of rotation, thus avoiding excessive stresses thereto.

The flexibility of the material would of course allow flexing in thecorrect direction of rotation as well, but the curvature of the vanes113, which matches the fluid threads that form during the rotation ofthe impeller, causes deformation in the correct direction of rotation tobe very limited in practice.

With reference to FIG. 6, in a third embodiment the impeller accordingto the invention comprises a disk 210 with a cup-shaped central hollowbody 211 which is a component of a driving device 212 similar to the oneof the first embodiment.

A plurality of vanes 213 protrudes from a ring 216 which is arranged onthe outside of the cup-shaped body 211 in a corresponding seat 210 a ofthe disk 210.

The vanes 213 are monolithic with respect to the ring 216, which affectsonly the part of said vanes that lies closest to the center.

The peripheral part can therefore perform flexing movements arising fromthe characteristics of the material of which the vanes are made.

The vanes 213 can also be rigidly coupled to the ring 216 (axial andtorsional retention) in various manners: by interlocking and/orinterference, ultrasonic welding, adhesive bonding.

The peripheral regions 214 of the vanes 213 are therefore, as mentioned,flexibly deformable, and said deformation is greater for the wrongdirection of rotation and is limited by teeth 215 which protrude fromthe disk 210 alternately with the vanes 213.

In order to center the vanes 213 with respect to the teeth 214, the ring216 has axial teeth 217 to be inserted in appropriately provided holes218 of the disk 210.

Also in this case, the cover 219 is separate from the ring 216, but itis also possible to provide alternative embodiments in which the cover219 is monolithic with the ring 216.

In this embodiment, the lid 219 of the hollow body 211 has, at its end,a seat 230 for a first shim ring 231 made of ceramic material, sinteredmaterial or similar hard material.

A second shim ring 232 made of ceramic material, sintered material orsimilar hard material is accommodated in a seat 233 provided at the endof a cylindrical support 234 which is supported by a bush 235 which isrigidly coupled, by means of radial spokes 236, to a ring 237 which isinserted with interference in a corresponding seat 238 of the volute229.

As an alternative, the support 234 can be monolithic with the bush 235.

The ring 232 acts as an axial thrust bearing in order to adjust, incooperation with the ring 231, the position that the impeller assumes inthe volute 229 and maximize hydraulic efficiency.

With reference now to FIG. 7, said figure is a chart which plots theflow-rate as a function of power and wherein:

the line D is the curve related to an impeller with the flexible vanesaccording to the invention, with the wrong direction of rotation;

the line C represents the maximum power that the motor can deliver;

the line A plots the curve related to an impeller with flexible vanes,in the correct direction of rotation.

The line D clearly shows that for any flow-rate in the wrong directionof rotation, the flexible vane requires more power than the motor cangenerate (straight line C).

Accordingly, the motor cannot start in the wrong direction.

FIGS. 8 to 10 illustrate another possible configuration of the impeller.

In this case, the impeller according to the invention, which is entirelymade of plastics, is generally designated by the reference numeral 310and comprises a first disk-like element 311 (which is monolithic withrespect to a bush 311 a) which monolithically supports, in this case,three curved nondeformable vanes 312 which are angularly equidistantand, at the center, a rounded shank (which is separated from their inletregion).

The impeller 310 further comprises an annular element 314, whosedimensions are contained within the inlet dimensions of saidnondeformable vanes 312; said annular element has means 315 (describedin greater detail hereinafter) for coupling to said first disk-likeelement 311.

The annular element 314 supports, so that they cantilever outward inthis case, three curved flexibly deformable vanes 316 which areangularly equidistant and are to be arranged alternately with thenondeformable vanes 312.

The annular element 314 is in fact accommodated in a complimentarilyshaped seat 317 of the first disk-like element.

The flexibly deformable vanes 316 end externally with respect to thedimensions of the nondeformable vanes 312, with respect to which theyhave slightly smaller axial dimensions.

The flexibly deformable vanes 316 are adapted to modify, when loaded,their curvature in one direction of rotation so that the power requiredfor rotation in that direction is higher than the maximum power that themotor (not shown for the sake of simplicity) can deliver.

The impeller 310 further comprises a second disk-like element 318, whichencloses, together with said first disk-like element 311, the set ofvanes 312 and 316 and is rigidly coupled, by ultrasonic welding,adhesive bonding or other known methods, to the nondeformable vanes 312,leaving free the flexibly deformable vanes 316, which have slightlysmaller axial dimensions.

The second disk-like element 318 has a central hole and its edge 319protrudes axially so as to form the inlet region for the fluid to bepumped.

As regards the coupling means 315, they comprise a shaped portion 320which is for example polygonal (dodecagonal in the figures), is providedon the internal surface of the annular element 314, and mates with acomplementarily shaped surface 321 of the seat 317.

The coupling means 315 comprise a specific number of tabs 322 which aresubstantially radial, are angularly equidistant, protrude from theannular element 314, are inserted between the vanes 316 and end withrespective axially elongated hooks 323, which engage by snap action,after elastic deformation, the first disk-like element 311 by insertionin suitable through holes 324 thereof.

The seat 317 of course has a shape which also accommodates the tabs 322.

The hooks 323 inserted in the through holes 324 prevent any axialmovement of the assembly constituted by the disk 314 and the vanes 316.

The coupling means 315 determine the exact mutual positioning of thevanes 312 and 316.

The peripheral part of the vanes 316 can thus perform flexing movementswhich arise from the elastic characteristics of the plastic material ofwhich they are made.

The deformation is greater for the wrong direction of rotation, and thevanes 316 modify their curvature so that in practice they block therotation.

The flexibility of the material would of course also allow flexing inthe correct direction of rotation, but the curvature of the vanes 316,which matches the fluid threads that form during the rotation of theimpeller 310, causes the deformation in the correct direction ofrotation to be very small in practice.

In practice it has been observed that the intended aim and objects ofthe present invention have been achieved.

With the flexible-vane impeller, monodirectionality is in fact ensuredfor all flow-rates/heads.

This is achieved in a constructively simple manner and has no effect onnoise levels.

The invention thus conceived is susceptible of numerous modificationsand variations, all of which are within the scope of the inventiveconcept.

Thus, for example, the change in the curvature of the vanes can beprovided by means of a hinge, even of the film type, which connects eachperipheral part to the central one.

In the embodiment of FIGS. 8, 9 and 10, even if the flexible vanes yielddue to wear, the nondeformable vanes continue to give their constantcontribution to the pumping action.

All the details may further be replaced with other technicallyequivalent elements.

In practice, the materials employed, so long as they are compatible withthe contingent use, as well as the dimensions, may be any according torequirements.

What is claimed is:
 1. A monodirectional impeller for centrifugalelectric pumps having a permanent-magnet synchronous motor, comprising:a first disk-like element, which is monolithically provided with curvednondeformable vanes; an annular element, whose dimensions are containedwithin inlet dimensions of said nondeformable vanes, said annularelement being provided with means for coupling to said first disk-likeelement, said annular element having flexibly deformable vanes whichcantilever outward and are interposed between the nondeformable vanes,said deformable vanes being adapted to modify, when loaded, theircurvature in both directions of rotation, so that the power required forrotation in only one of the two directions is greater than a maximumpower that the motor can deliver; and a second disk-like element rigidlycoupled to said nondeformable vanes; wherein said first disk-likeelement and said second disk-like element enclose said deformable andnon-deformable vanes, and leave the flexibly deformable vanes free. 2.The impeller according to claim 1, wherein said first disk-like elementis monolithically provided with curved nondeformable vanes which areangularly equidistant.
 3. The impeller according to claim 2, whereinsaid shaped portion is polygonal.
 4. The impeller according to claim 1,wherein said first disk-like element is monolithically provided, at acenter, with a rounded shank which is shaped so as to facilitatecoupling with the deformable vanes, said shank being separate from theinlet region of said nondeformable vanes.
 5. The impeller according toclaim 4, wherein said coupling means comprise substantially radial tabswhich protrude from said annular element, are angularly equidistant andend with respective axially elongated hooks which engage with a snapaction said first disk-like element by insertion in suitable throughholes of said first disk-like element.
 6. The impeller according toclaim 1, wherein said flexibly deformable vanes; cantilever outward andare interposed between the nondeformable vanes.
 7. The impelleraccording to claim 1, wherein said annular element is accommodated in acomplementarily shaped seat of said first disk-like element.
 8. Theimpeller according to claim 1, wherein said flexibly deformable vanesend outside the dimensions of the nondeformable vanes.
 9. The impelleraccording to claim 1, wherein said deformable vanes have slightlysmaller axial dimensions than the nondeformable vanes.
 10. The impelleraccording to claim 1, wherein said second element is rigidly coupled tosaid first element by at least one of ultrasonic welding and adhesivebonding.
 11. The impeller according to claim 1, wherein said seconddisk-like element is provided with a central hole and its edge protrudesaxially so as to form the inlet region for the fluid to be pumped. 12.The impeller according to claim 1, wherein said means for mutuallycoupling said first disk-like element and said annular element comprisea shaped portion which is provided on the internal surface of saidannular element and mates with a complementarily shaped surface of itsseat.
 13. The impeller according to claim 1, wherein said means farmutually coupling said first disk-like element and said annular elementcomprise at least one tab which protrudes from said annular element andends with an axially elongated hook which engages with a snap action,after elastic deformation, said first disk-like element by insertion ina suitable through hole of said first disk-like element.